Japanese Unexamined (Kokai) Utility Model Publication No. 62-183082, published on Nov. 20, 1987 by the Japanese Patent Office, discloses a variable capacity swash plate type compressor having single headed pistons therein. The variable capacity swash plate type compressor of Japanese Unexamined Utility Model Publication '082 includes a cylinder block having a crank chamber formed therein for housing an inclination changeable wobble plate assembly, and a plurality of cylinder bores in which a plurality of single headed pistons are reciprocally fitted, to suck and compress a refrigerant gas and to discharge the compressed refrigerant gas. The wobble plate assembly includes a rotary drive element rotatable with the drive shaft and a swash plate non-rotatably supported on the rotary drive element, and is driven by a rotatably supported axial drive shaft to which a lug member is fixedly attached to be projected radially and rotated together with the drive shaft within the crank chamber. The lug member is operatively connected to the rotary drive element of the wobble plate assembly via a hinge mechanism, and a sleeve element slidably mounted on the drive shaft is also operatively connected to the rotary drive element of the wobble plate assembly. Namely, the rotary drive element is able to be rotated together with the drive shaft and to change an angle of inclination thereof from an erect position corresponding to a small compression capacity position to a fully inclined position corresponding to a large compression capacity position. The hinge mechanism includes an elongated guide hole bored through the lug member, and a hinge pin having one end movably fitted in the elongated guide hole of the lug member and the other end fixed to a swing plate member extended from the rotary drive plate. The sleeve element is arranged to be axially slid, and provided with a lateral pin radially projected therefrom to form trunnion pins about which the rotary drive plate is pivotally mounted. The swash plate of the wobble plate assembly is operatively connected to the plurality of pistons via respective piston rods having ball-and-socket joints on both ends, and thus, when the drive shaft is rotated, the rotation of the drive shaft and the rotary drive element is converted into a reciprocation of the respective pistons in the cylinder bores. The cylinder block has a communication passageway formed therein and extended between the crank chamber and a suction chamber, for receiving therein the refrigerant gas before compression and an extent of the communication between the abovementioned two chambers is controlled by a capacity control valve.
With the above-mentioned compressor, when the respective pistons are reciprocated in response to the rotation of the drive shaft, the refrigerant gas before compression is pumped from the suction chamber into the cylinder bores, to be compressed by the pistons during the suction and compression strokes of the pistons, and the compressed gas is discharged from the cylinder bores toward a discharge chamber for the refrigerant gas after compression. During the operation of the compressor, a force consisting of first and second forces acts on the wobble plate assembly from the pistons, as a reaction of the compression and suction of the refrigerant gas by the pistons, and the wobble plate assembly is physically supported by the hinge mechanism at a fulcrum position thereof at which the hinge pin is in contact with the guide wall of the elongated guide hole of the lug member.
The construction of the above-mentioned hinge mechanism including the projected lug member radially projected from the drive shaft and the hinge pin in engagement with the elongated hole of the lug member results in an arrangement such that the fulcrum position of the hinge mechanism is moved around the axis of the drive shaft so as to constantly correspond to a given position of the swash plate at which the swash plate is connected to one of the pistons moved in the cylinder bore to the top dead center "T" thereof from the bottom dead center "B," thereof, as diagrammatically illustrated in FIG. 6 of the accompanying drawings, during the rotation of the rotary drive element of the wobble plate assembly. Nevertheless, when each of the pistons approaches the top dead center "T" thereof during the reciprocation thereof, the discharge of the compressed refrigerant gas from the cylinder bore toward the discharge chamber is completed, and as soon as the movement of the piston is reversed at the top dead center "T", the suction of the refrigerant gas before compression is subsequently carried out for a time between "T" and "B.sub.2 " of FIG. 6. Therefore, when each piston is moved between the bottom dead position "B.sub.1 " and the top dead center "T", the piston applies the first force to the swash plate, as a reaction of the compression of the refrigerant gas, and when the piston is moved between the top dead center "T" and the bottom dead center "B.sub.2 " the piston applies the second force to the swash plate, as a reaction of the suction of the refrigerant gas. Accordingly, the total force of the first and second forces acting from each piston on the wobble plate assembly is concentrated at a position of the assembly shifted from the fulcrum position "P" of the hinge mechanism in a direction of the rotation of the rotary drive plate of the wobble plate assembly, and an amount of the shift depends on the number of rotations of the drive shaft, and the compression ratio of the refrigerant gas or the angle of inclination of the wobble plate assembly. Therefore, the wobble plate assembly supported by the fulcrum position of the hinge mechanism must be subjected to a bending moment due to the shifting of the position at which the total force of the first and second reaction forces acts on the wobble plate assembly from the fulcrum position of the hinge mechanism. This bending moment acting on the wobble plate assembly is absorbed by the sleeve element to thereby apply an excessive local force to the sleeve element, and as a result, an abnormal noise is generated when the sleeve is slid on the drive shaft and the physical durability of the sleeve element is reduced.